1. Field of the Invention
The present invention relates to an improved antenna disposition structure for a motorcycle.
2. Description of the Background Art
A technique of performing radio communication between vehicles for detecting the presence of another vehicle has been disclosed, for example, in Japanese Patent Laid-open No. Hei 11-352221 entitled xe2x80x9cMovable Body Detecting Systemxe2x80x9d. According to this technique, the vehicle concerned transmits a vehicle identification (ID) code signal and receives a vehicle identification (ID) code signal transmitted by a different vehicle, thereby recognizing the presence of the different vehicle and measuring a distance therebetween.
The transmission and reception of such a vehicle identification (ID) code signal requires radio communication via an antenna. The mounting position of an antenna on a vehicle is significantly restricted, if the vehicle is configured as a motorcycle having a small vehicular body.
An antenna disposition structure is disclosed, for example, in Japanese Utility Model Laid-open No. Sho 63-91991 entitled xe2x80x9cFoldable Antenna for Motorcyclexe2x80x9d. As shown in FIG. 1 of that document, a foldable antenna is provided on a portion near a rear carrier of a large-sized motorcycle in such a manner as to extend upwardly therefrom.
In order to efficiently transmit a large amount of data including a vehicle identification (ID) code signal, a signal indicating a running state of the vehicle, and a coordinate signal indicating a position of a running vehicle, in a short time by using radio waves, the wavelengths of the radio waves may desirably be shorter. In actual use, microwaves having ultra high or higher frequencies have been desirably used for radio communication between vehicles. Such microwaves, however, have a very strong rectilinear propagation property, and therefore, they are liable to be shielded by obstacles present in the rectilinear path of the microwaves.
If an antenna is provided behind a passenger, for example, as disclosed in Japanese Utility Model Laid-open No. Sho 63-91991, microwaves traveling from the front of the vehicle to the antenna are shielded by a windshield and the passenger. In this way, from the viewpoint of reception of signals transmitted from the front of the vehicle via microwaves, the disposition of an antenna behind a passenger is undesirable.
It is therefore an object of the present invention to provide an antenna disposition structure suitable for a motorcycle. To achieve the above object, an antenna disposition structure is provided for a motorcycle including an antenna for radio communication, wherein the antenna is disposed over a headlamp and forwardly from a virtual slant line connecting the center of a handlebar to an axle of a front wheel.
With this configuration, the antenna can be sufficiently separated from a driver of the motorcycle. A driver, who functions as a body absorbing radio waves, acts to weaken radio waves. According to this configuration, however, since the antenna is disposed forwardly from the slant line, it is possible to prevent the effect of absorption of radio waves by a driver and to prevent reductions in electromagnetic fields in the vertical and horizontal directions.
The antenna provided over the headlamp is located at a sufficiently high position, and such an antenna can ensure good line-of-sight of a large number of objects to or from which radio waves are transmitted or received without interference with obstacles on a road. As a result, the reliability of communication by means of the antenna can be enhanced.
The antenna may be covered with a front cover made of resin or a resin-molded product equivalent thereto. With this configuration, the antenna can be mounted by making effective use of a space in the front cover, and the front cover formed of a resin-molded product allows the passing of radio waves therethrough, and can desirably protect the antenna. For example, the front cover prevents the antenna from being damaged due to rain and wind and being broken due to contact with another movable body. Further, since the antenna is not exposed from the front cover, it is possible to keep a good external appearance of the vehicle.
The antenna may be mounted on an upper edge portion of the headlamp. With this configuration, since the antenna is mounted on the upper edge portion of the headlamp, a reflection body such as a metal from which radio waves are reflected, and/or an absorption body such as a human being which absorbs radio waves, are not present in the surroundings of the antenna, particularly, in front of and above the vehicle. As a result, it is possible to prevent a reduction in intensity of radio waves transmitted or received by the antenna.
A horizontal base may be provided on an upper edge portion of the headlamp or over the headlamp, and the antenna is mounted on the mounting base. With this configuration, the antenna can be easily mounted to the headlamp irrespective of the shape of the headlamp. As a result, one kind of antenna can be applied to various kinds of motorcycles.
The front cover may be provided under the handlebar, and a containing space provided in the front cover at a position over the headlamp. An opening communicated to the containing space is provided in the front cover, the opening being covered with a lid. A horizontal mounting base is provided in the containing space on an upper edge portion of the headlamp or over the headlamp, and the antenna is mounted on the mounting base. With this configuration, since the containing space is provided in the front cover, the antenna can be mounted by making effective use of the space in the front cover.
Since the front cover is made from a resin, it can protect the antenna while allowing the passing of radio waves therethrough. For example, the front cover prevents the antenna from being damaged due to rain and wind and being broken due to contact with another movable body. Since the antenna is disposed at a position higher than the headlamp, it can receive radio waves without interference with obstacles on a road. As a result, the reliability of communication by means of the antenna can be enhanced. Further, since the opening of the containing space is covered with the front lid, the maintenance of the antenna in the containing space can be easily performed.
The antenna may have a forward directivity with respect to the running direction of the motorcycle. With this configuration, if the antenna is taken as an antenna for radio communication between vehicles, since the antenna has the forward directivity, it can achieve desirable radio communication with another vehicle running ahead of the vehicle concerned.
The antenna may be composed of a first antenna and a second antenna disposed adjacently to each other, wherein the first antenna has a forward directivity with respect to the running direction of the motorcycle, and the second antenna has an upward directivity with respect to the running direction of the motorcycle. With this configuration, if the first antenna is a transmitting/receiving antenna for radio communication with another vehicle, and the second antenna is a receiving antenna for the GPS, it is possible to desirably perform radio communication with another vehicle running ahead of the vehicle concerned by the first antenna and desirably receive radio waves from a number of artificial satellites by the second antenna, and hence to obtain accurate positional information of the vehicle concerned.
Further, since the first and second antennas are disposed adjacent to each other, they can be contained in a compact containing space. Also, if the first and second antennas are covered with a protective cover for improving the weather resistance, the protective cover can be miniaturized and thereby can be made inconspicuous. Since the first and second antennas are not exposed and further the protective cover is made inconspicuous as described above, it is possible to maintain a good external appearance of the vehicle.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.